As wireless communication systems have become ubiquitous, people have an increasing demand for high data rates (especially, up to 10 Gbps) to get a better user experience. Such high data rates require a very wide range of bandwidths which can only provided in a millimeter-wave band. This means a kind of wireless communication networks operating in the millimeter-wave band (hereinafter referred to 5G RAT networks) will appear and become more and more popular in the future. However, path loss in such 5G RAT networks is usually very serious due to high frequencies. Therefore, in order to mitigate the path loss, directional transmission (i.e. high-gain beamforming) realized with an antennas array is typically employed in communication apparatuses (e.g. Access Nodes, User Equipments) in the 5G RAT networks to transmit and/or receive data and/or instructions.
Besides traditional licensed exclusive millimeter-wave bands, 5G RAT networks are also expected to operate in unlicensed millimeter-wave bands which are usually shared between different links, operators, communication systems, and so on. In this case, a mechanism for sharing spectrum/channel is needed in the 5G RAT networks to avoid interference between different communication links.
Existing Wi-Fi wireless communication networks are based on IEEE 802.11 standards and generally employ a Listen Before Talk (hereinafter, referred to LBT) mechanism (e.g. a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)) to enable spectrum/channel sharing. According to the LBT mechanism, if a communication apparatus is going to transmit data, it should at first listen to a shared channel to determine whether the shared channel is idle, and transmit data only when the shared channel is idle. The LBT mechanism works well in Wi-Fi wireless communication networks since communication apparatuses in these Wi-Fi wireless communication networks operate in low frequencies and typically employ omni or quasi-omni directional transmission to transmit and/or receive data and/or instructions. However, as mentioned above, 5G RAT networks operate in much higher frequencies and typically employ directional transmission to transmit and receive data and/or instructions which are different from Wi-Fi wireless communication networks. Therefore, the LBT mechanism might not work well in 5G RAT networks.